Internal combustion engines operating on a two-cycle principal have traditionally been arranged so that fuel is delivered into an incoming air supply. The fuel and air mixture passes into a crankcase chamber for crankcase compression, and is then delivered through a scavenge passage to a combustion chamber of the engine for combustion therein.
As is well known, in the operating cycle of a two-cycle engine, an exhaust port leading from the combustion chamber is open during at least part of the time the scavenge passage is open. Thus, exhaust along with a portion of the air and fuel charge delivered through the scavenge passage flows through the exhaust port into the exhaust system.
In this arrangement, and especially at low engine speeds, a large amount of fuel must be added to the air to compensate for the flow of fuel through the cylinder and directly out the exhaust port. Supplying excessive fuel, however, is costly and can result in stalling of the engine. In addition, the quantities of fuel flowing into the exhaust may foul a catalyst positioned in the exhaust system.
As one attempt to solve the above-stated problems, some two-cycle engines are arranged to have fuel directly injected into the combustion chamber. A fresh air charge is supplied to each combustion chamber through the crankcase and a scavenge port. Once air is supplied to the combustion chamber and the exhaust port is closed, a fuel injector injects fuel directly into the combustion chamber for mixing with the air.
This arrangement has the benefit that little of the fuel flows unburned into the exhaust system, and the amount of fuel supplied to each combustion chamber may be more closely controlled. In many instances, these injectors are of the pressure activated type, where the injector valve only opens when the pressure of the fuel being supplied is high enough. Thus, these systems have a fuel supply which includes a fuel tank and a high pressure pump for pumping fuel from the tank and supplying it under high pressure to the fuel injector.
One problem with these systems is that the pressure of the fuel in the system must be accurately controlled in order to control the injection timing and duration. An electrically operated high pressure pump of variable speed may be used for this purpose. This arrangement, however, requires a complex control for the pump. In addition, the electrically powered pump is susceptible to failure, especially when operated in high temperature environments, such as in the cowling of an outboard motor. An additional problem is that the heat generated by the pump increases the temperature of the fuel and makes more likely the inclusion of vapor within the system.
A mechanical pump is more reliable in this type of environment. Such a pump, however, is driven at speed which corresponds to the speed of the engine. Thus, if the pump is arranged to provide sufficient fuel at a pressure which will open the injectors when the engine is at low speed, when the engine reaches higher speeds, the pump is likely to provide fuel at much too high of a pressure. At the high speeds, fuel is then delivered too long and/or in too great of a quantity. In addition, the high pressure within the fuel system may result in fuel leaks.
A fuel injection system for delivering fuel from a fuel source to a combustion chamber of an engine through a fuel injector which overcomes the above-stated problems is desired.